This invention relates to filter connectors and, more particularly to a filter connector with a latchable mounting frame.
Electronic circuits for use in, for example, motor vehicles have to meet high standards as regards shielding against interference signals. The interference signals produced in an automobile while it is running extend over a broad frequency range, i.e., from a few Hz to several MHz.
Filter connectors are commonly used in motor vehicles to suppress interference signals which occur between interconnections of various electronic units. Copending U.S. patent application Ser. No. 07/318,149, filed Mar. 2, 1989 and assigned to the same assignee as the present application, describes a filter connector with effective shielding against interference signals of relatively low frequency and with a filter unit having filter capacitors which suppress interference signals of relatively high frequency. The filter unit is similar to that also disclosed in assignee's U.S. Pat. No. 4,791,391 wherein the filter capacitors are separately formed on an alumina substrate around a plurality of apertures. A pin terminal is mounted in each aperture and is an electrical contact with the filter capacitor surrounding that aperture. A ground electrode is formed around the periphery of the substrate.
Such filter connectors are normally mounted to a grounding chassis. It is advantageous that the filter connectors be easily mountable and removable for repair. One means of mounting such filter connectors in a motor vehicle is disclosed in U.S. patent application Ser. No. 07/370,836 filed June 23, 1989, also assigned to the same assignee as the present application and now abandoned. In this application, the filter unit substrate of the filter connector is mounted with one of its flat side in contact with the chassis. This accomplished through the use of a holder or frame of electrically conducting material which engages the other flat side of the filter unit substrate. The frame has mounting lips which can be bent over to secure it to the chassis. The chassis in the aforenoted application is formed of two dish shaped shells of sheet metal between which electronic components are disposed for shielding against interference signals.
For effective shielding against interference signals, it is desirable for the filter unit substrate to be in electrical contact with the chassis to which it is mounted along the entire periphery of the filter unit substrate. When the chassis is formed of sheet metal, such as disclosed in the aforenoted U.S. application Ser. No. 07/370,836, this is generally easy to achieve since the surface of sheet metal can be formed with sufficient accuracy by means of pressing or punching. Surface accuracy is important to avoid undesirable mechanical stresses on the filter substrate when it is mounted. This is particularly important in the case of substrates of ceramic material such as alumina, which are generally fairly brittle and are thus susceptible to cracks and breakage.
Sheet metal chassis cannot be used for car telephones such as modern cellular telephones. Filter connectors are important in such car telephones to provide electric coupling between the transmitter and receiver housing parts, which are fitted in separate, shielded compartments. In the case of such car telephones, cast aluminum parts are used for the chassis. Since all openings and mounting faces are made by casting, machine finishing of the mounting faces to obtain a desired surface accuracy for mounting filter connectors is too expensive in practice. Mounting the filter connector for effective shielding is therefore considerably more difficult when a case metal chassis is used.